1. Field of the invention
The present invention relates to a process for the production of spherical ceramic granules.
2. Description of the Related Art
Hitherto, as the production method of porous ceramic granules, there are well-known the following methods:
1) the method in which a slurry of the starting ceramic powders is mixed with a foaming agent such as hydrogen peroxide and the like, the mixture is heated at about 70 to 120.degree. C. to dry the mixture along with foaming, and the dried and foamed product is pulverized after firing; PA1 2) the method in which a slurry of the starting ceramic powders is mixed with a thermally dissipatable substance, and the mixture is pulverized after drying and firing; and PA1 3) the method in which a slurry of the starting ceramic powders is mixed with a thermally dissipatable substance acting as a thickening agent and, if desired, a foaming agent, the mixture is stirred to cause thickening or gelation of the slurry, and the slurry is dried while retaining the generated foams therein, and, if desired, calcinating the same, and the dried product is subjected to a pulverizing and firing process in any desired order (see, Japanese Unexamined Patent Publication No. 3-252304). Among these three methods, in particular, the third method enables the production of porous ceramic granules having a high porosity which contain, in addition to spherical micropores produced upon foaming, three-dimensionally communicating micropores formed between the adjacent particles of the starting ceramic powders. PA1 pulverizing a dried product of a ceramic material; PA1 calcinating the pulverized product at a temperature of about 300 to 900.degree. C.; PA1 rotating the calcinated granules to make spherical granules; and PA1 firing the spherical granules. PA1 pulverizing a dried product of a ceramic material; PA1 calcinating the pulverized product at a temperature of about 300 to 900.degree. C.; PA1 filling said resulting granules in a container; PA1 rotating the container so that the granules are converted to spherical granules, and PA1 firing the spherical granules.
However, the granules formed by these prior art methods have a drawback that the shape of the granules is still similar to the shape after the pulverizing process. That is, just after pulverization, the granular particles still have sharp edge portions which cause a reduction of the fluidity of the particles, and thus an insufficient operability of the granules has been a problem to be solved.